In a typical pump for pumping a fluid such as water, oil or the like and, in particular, an axial flow pump, a plurality of blades or impellors are arranged on a shaft in circumferentially spaced relationship so that rotation of the blades by the shaft produce a pumping action on the fluid, the pitch of the blades determining the output of the pump. Such blades are generally securely mounted on the shaft and perform a fluid pumping operation regardless of the viscosity of the pumped fluid or the resistance to fluid flow in the pipe line in which the pump is installed. Thus, although the blades may be designed for maximum efficiency under certain average conditions, when unusual conditions develop such as a change in fluid viscosity or when a change in fluid flow resistance or the like, the efficiency of the pump becomes somewhat less than that desired increasing the comsumption of power and the wear and tear on the pump. Furthermore, it is not unusual for the pump driving motor to stop suddenly due to a power interruption or the like during a pumping operation with the attendant application of detrimental forces on the blades or on accessories such as pipelines associated with the propeller.